| 摘要 |
PURPOSE:To prevent flase announcing due to various noises completely by taking out the noise component from a reception signal, removing the noises from the reception signal and obtaining only the original detection signal. CONSTITUTION:An oscillator 1 generates the detection signal of a frequency f0. This detection signal is applied to an excitor 2, and a detection line 3 is disposed to the excitor 2 by leaving a suitable spacing therefrom. A notch filter 11 and a subtractor 12 are connected to the line 3. The filter 1 is so constituted as to block the frequency f0 and to allow the passage of the noise of frequency other than this and is so constituted as to transmit only the detection signal of the frequency f0 to a subsequent detection circuit 5, etc., by removing the noise components from the reception signal with a subsequent subtractor 12. Thereby, the noise components are removed from the reception signal and therefore a beat which is the cause for fases announcing is not generated, and the possibility of causing malfunction through a comparator 7 is eliminated. |
